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preroll music
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Herald: It's simple when ice gets above
0°, it melts. But is it really that simple
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if we are not talking about a small ice
cube, but a big sheet of ice covering an
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entire continent? Is that really the only
factor? And, am I right with my
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assessment? I'm looking forward to be
enlightened by Professor Doctor Ricarda
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Winkelmann. Ricarda Winkelmann is a
professor of climate science at the
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University of Potsdam, and she's also a
researcher for climate impact. She leads
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the Ice Dynamics Working Group and Co-
leads PIK Future Lab on Earth Resilience
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in the Anthropocene. Her research focuses
on tipping elements from the Earth system.
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And today she'll be talking about the
Greenland and Antarctic ice dynamics and
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the future sea level rise that are
impacted by them. It appears like she's
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surely an expert on all things related to
ice. So please give a warm hand of
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applause for Professor Doctor Ricarda
Winkelman with her talk: "The Big Melt:
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Tipping Points in Greenland and
Antarctica" Have fun!
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[no audio]
in between music
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Ricarda Winkelmann: audio not working
Thanks and welcome. Today, we're going to
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take a little excursion to the far north
and the far south, to our polar ice sheets
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on Greenland and Antarctica. As this year
is coming to a close, I thought we'd take
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a brief moment to reflect back. 2020 has
certainly been an exceptional year for all
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of us. It was supposed to be a super year
for nature and the environment, as world
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leaders put it at the beginning of the
year. It's five years after the Paris
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climate accord. It's five years after the
Sustainable Development Goals have been
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announced. However, 2020 turned out to be
the year when we've had to face several
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global crises, including the ongoing
covid-19 pandemic and also the ongoing
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climate crisis. What almost got lost in
the turmoil is that this year also saw
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several weather and climate extremes,
which spaned the globe from pole to pole,
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with temperatures reaching record highs in
the Arctic and Antarctica with +38°C in
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the Arctic and in Siberia. That's the
highest temperature that was ever recorded
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north of the Arctic Circle and it's
roughly 18° warmer than the average
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maximum daily temperature in June, when
this was recorded. And we also saw +18° at
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the Antarctic Peninsula, which is, again,
the highest temperature ever recorded in
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Antarctica. And this was followed by
widespread melting on nearby glaciers.
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Now, if we're kind of zooming out and
taking a look at the bigger picture, we're
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also at a very significant point in
Earth's history. Here you see the global
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mean temperature evolution since the last glacial
maximum. So the last ice age until today.
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And whenever I look at this graph, I see
two things that still strike me to this
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day. One is that the Holocene, the
interglacial or the warm age, in which
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human civilizations have developed and
thrived, has been characterized by very
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stable climate conditions, by a very
stable global mean temperature. And the
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other thing is that the difference between
an ice age, here, 20 000 years ago
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roughly, and a warm age, that's roughly
three to four degrees of global average
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temperature change. And right now we're on
the verge of achieving the same
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temperature difference, but at much, much
faster rates. So here you see several
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future temperature projections from the
IPCC. And what you can see is, that in all
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of them, the temperature increase, even
the lowest one, the temperature increase
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is much faster than it was ever recorded
before. So I think it's safe to say that
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we have truly entered the Anthropocene and
that humans have become a geological
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force. So in the Anthropocene, humans have
become the single most important driver of
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global change affecting the entire Earth
system, including our ice sheets. But it
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was kind of the opposite in the past. Like
no other forces on the planet, ice ages
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have actually shaped our surroundings and
thereby determined our development as
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human civilizations. For instance, we owe
our fertile soils, to the last ice age,
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that also carved our current landscapes
that we see all around us, leaving
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glaciers behind, rivers and lakes. So even
though the ice sheets on Greenland and
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Antarctica might seem far away sometimes,
they're actually crucial also for us here
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today. And today, I want to leave you with
an impression why they are so important.
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And one reason why they are so important
is because they're an amazing climate
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archive. Here you see an ice core taken
from one of the deepest parts of an ice
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sheet. And this is basically like counting
tree rings. You can go back to the past
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and you can see what the climate was like
in the deep past, ranging several hundreds
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of thousands of years back. And you can
see the conditions, for instance, in the
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CO2 change, the temperature change over
this really long timescales. So that's one
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of the reasons why the ice sheets are so
important. Another one is their so-called
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sea level potential. Greenland and
Antarctica are truly sleeping giants. And
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to give you an idea of the sheer size of
these two ice sheets, one way of doing
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that is to compute their ice volume in the
so-called sea level equivalent. What this
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means is, if we were to melt down the
Greenland ice sheet and distribute that
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meltwater around the entire globe, then
this would lead to a global sea level rise
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of roughly seven meters. For the West
Antarctic ice sheet, it's about five
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meters, and for East Antarctica, the
tenfold. So more than sixty five meters in
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total of sea level potential that are
stored in these two ice sheets. Now, over
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the past decades, the ice sheets have both
been losing mass and they've been losing
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mass at an accelerating pace. In fact,
we're currently on track with the worst
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case climate change scenario. Here you see
the observations in gray and you also see
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several of the projections from the past
for the ice sheets. And as you can see,
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we're tracking this upper branch here. So
we're really on track with the worst case
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climate change scenario for the ice
sheets. And what this means is even if we
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were to stop global warming today, the ice
sheets would still keep losing mass
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because of the inertia in the system. So
sea levels would keep rising for decades
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or even centuries to come. Why is that?
Well, there are several processes that we
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need to understand in order to keep track
of sea level change and also to understand
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the ice sheet's evolution in the past and
in the future. Here, you see sort of an
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exemplary cut through an ice shelf system,
where the ice sheet is in contact with the
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atmosphere. You have a grounded part and
then in many places, you also have these
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extensions, these floating extensions, the
so-called ice shelves that surround
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particularly Antarctica. The separation
between the two is the so-called grounding
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line. Now, generally ice sheets gain mass
through snowfall just on top of the ice
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sheet, which then is compressed into ice
and over time, due to the sheer gravity
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and the sheer size of the ice sheets, it's
basically pushing its own mass towards the
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ocean. And that's one of the reasons why
there's a constant flow of ice. So ice is
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really not only a solid, it's also a
fluid. The ice sheets can also lose mass
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through surface melting, but also through
melting at the underside of the floating
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ice shelves, where they're in contact with
warmer ocean waters. And then there can,
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of course, also be ice shelf calving, so
icebergs that break off at the margins of
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the ice sheet. Now, what we see here, this
left hand side, that's a typical situation
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for the Greenland ice sheet. The Greenland
ice sheet is generally grounded above sea
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level in most parts and it's not only much
smaller than Antarctica, but it's also
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located further south, so further away
from the pole. And that means it's
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generally warmer in Greenland, leading to
more surface melt for the Greenland ice
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sheet. Whereas in Antarctica, it's not
only much colder there, but also the ice
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sheet is covered and surrounded by
floating ice shelves almost all around the
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coastline. And that means that one of the
most important driving processes for mass
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loss in Antarctica is this melting
underneath the ice shelves, so the
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subshelf melting in contact with the
warmer ocean waters. Just to give you an
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impression of the sheer ice thickness, I
brought this picture here. This is my very
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first impression of the Antarctic
coastline, the ice shelf margin. This is
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close to the German research station
Neumayer III. And I will never forget the
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moment that I first saw the ice shelf
edge. It was in the middle of the night,
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but we were there in summer, so we had
twenty four hours of daylight. And I woke
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up because it suddenly got dark in our
cabin. So I went up to the bridge to see
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what was going on and I saw myself in
front of a wall, like really a cliff of
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ice. And knowing that these ice shelves
behave like the ice cubes in the water
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glass, so only roughly 10 percent are
visible above the sea level, this means
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that in this case, we had an ice shelf
edge that was more than 100 meters thick.
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And that really impressed me. I
immediately had to think of this German
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expression, "das ewige Eis", the eternal
ice. And I really wondered if this is
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maybe the right expression because it
seemed like it was so static and nothing
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was moving. However, that's not true
because even in equilibrium, the ice is
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constantly moving. It's here just
visualized by these little snowflakes and
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you can see how the ice is moving from the
interior towards the coastlines. And we
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have a wide range of velocities at the
surface, ranging from almost zero in the
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interior of the ice sheet to several
kilometers per year in the larger ice
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shelves and also the so-called ice
streams, the faster flowing ice. If I were
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able to take a dive underneath the ice
shelves and I could actually take a look
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at the grounding line, this would probably
be what what I could see. This is the
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triple point basically where solid earth,
the ice and water all come together. And
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this grounding line is a very important
role for Antarctic ice dynamics and also
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for the future fate of Antarctica. So what
makes the dynamics of the ice sheets and
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shelves so particularly difficult to
understand and also to project the future
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evolution is that both ice sheets are
subject to several so-called positive, so
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self-reinforcing feedback mechanisms. Here
are just some examples with some of the
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major ones we know very well. One is the
ice-albedo-feedback and another one is the
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so-called melt-elevation-feedback. As I
said, in Greenland we observe a lot of
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surface melting. If you've ever flown
across the Greenland ice sheet in summer,
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you can really see these rivers forming
and then even lakes forming at the ice
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sheet surface. And over the recent decade,
Greenland has been subject to several
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extreme melt events, including
particularly the year 2010, 2012 and also
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last year. And the reason there's this
extreme melting at the surface is due to a
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combination of factors, it has to do with
the duration of the summer, but also even
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here in Europe, we observed very warm and
dry summers. And that's also something
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that was observed for Greenland. So that,
for instance, in the year 2019 in August,
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almost the entire ice sheet surface was
covered with meltwater. Now, why is this
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surface melting so important? The reason
is that there is also a self-reinforcing
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feedback that could be driven by surface
melting. And we all know this mechanism
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from mountain climbing. If you climb down
from the peak of a mountain towards the
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valley, it gets warmer around you. And the
same is true also for the ice sheets. So
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if there's enough melting, it could
actually lower the surface to a region
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where the temperatures are higher, the
surface temperatures are higher, leading
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to more melting, which again lowers the
surface elevation, leading to higher
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temperatures, leading to more melting and
so on and so on, so that this can trigger
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these self-reinforcing dynamics. And
whenever we have such a positive or self-
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reinforcing feedback mechanism, we can
also have a tipping point. And here is the
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depiction of a very simple way of
computing, where this tipping point might
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be for the Greenland ice sheet, where
we've really done this with just
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analytical work. So pen and paper, trying
to understand where we go from a stable
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Greenland ice sheet into unstable regime,
which would then lead to a meltdown of the
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entire ice sheet until basically no ice is
left at the surface. So this is something
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that we can understand in theory, but also
something that we find in more complex
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numerical ice sheet models. And they find
that this warming threshold that leads to
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basically a decay of the entire ice sheet
lies somewhere between 0.8°C and 3.2°C of
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warming above pre-industrial levels. And
you can see that between these
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temperatures, somewhere there's almost a
step change. This is now the computed sea
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level rise. So up here, this means that
Greenland is ice free. So we're going from
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an intact Greenland ice sheet to an ice
free Greenland somewhere between these
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temperatures. What this looks like can be
visualized with numerical ice sheet
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models. And here you see that once this
threshold is exceeded, basically the
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eigendynamics lead to a complete meltdown
off the ice sheet, until there's almost no
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ice left except for in the highest regions
here in the east where there are some
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small ice caps remaining. Now, something
similar, but also different is going on in
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Antarctica because, as I said earlier, in
Antarctica it's much colder. So we have
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very little surface melt at the moment.
But at the same time, it's surrounded by
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the floating ice shelves and they play the
major role in driving sea changes in
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Antarctica. Antarctic mass loss has
tripled over the recent years, especially
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in the so-called Amundson and
Bellingshausen Sea regions. So these are
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these regions here where you see all these
red parts. So this is all ice loss that's
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been detected here. And the reason for
this is due to the ice shelf ocean
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interactions. So here you now see the
ocean temperatures surrounding Antarctic
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ice shelves. And you can see a stark
difference between the temperatures here
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around the Amundson and Bellingshausen
regions and the temperatures, for
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instance, here in the Weddell Sea or in
the Ross Sea, the temperature difference
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being roughly two degrees. So there's
really been a switch from a colder to a
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warmer cavity, for instance, here in the
Amundson Sea region. And that drives more
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sub shelf melting, which in turn leads to
a decrease of the so-called buttressing
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effect. What this means is, well, first of
all, the ice shelves do not contribute to
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sea level rise directly, at least not
significantly. The reason being that they
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are like ice cubes in a water glass. And
if that melts down, it also doesn't raise
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the water level in the glass. So it's
similar with the ice shelves, but at the
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same time they are still attached to the
grounded part of the sheet. So if the ice
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shelves melt or there are larger calving
events in the ice shelves, that means that
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the flow behind them from the interior of
the ice sheet into the ocean accelerates.
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It's almost like pulling a plug. And this
is what is the so-called buttressing
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effects, so the backstress at the
grounding line. So if we have enhanced ice
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shelf melting, that means that this
buttressing effect, this buffering effect
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is reduced and therefore we have
accelerated outflow into the ocean. Now,
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the question is, how does this impact the
ice sheet dynamics overall, in particular,
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the stability of the West and East
Antarctic ice sheets. You may have come
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across some of these headlines in recent
years. My favorite one is still this one
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up here from 2014 where the "Holy Shit
Moment of Global Warming" was declared.
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And the reason for this were these
observations from the Amundson region in
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West Antarctica. So we're now taking sort
of a flight into the Amundson Sea region.
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And what was observed over the recent
decades is not only that the glaciers here
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have accelerated, so everything that's
shown in red is accelerated ice flow, but
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at the same time, the glaciers have also
retreated into the deeper valleys behind.
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So you see this browning at the surface
now. So all of these changes where the
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glaciers have basically retreated and with
this comes another self reinforcing
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feedback, the so-called marine ice-sheet
instability. For the marine ice sheet
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instability to occur, we need two
conditions to hold. One, as depicted here,
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is that the ice sheet is grounded below
sea level, which is true for many parts of
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West Antarctica, but also some parts of
East Antarctica. And also we need to
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generally have a retrograde sloping bed.
So that means that the bedrock elevation
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decreases towards the interior of the ice
sheet. And when these two conditions hold,
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then we can show in two dimensions,
mathematically, we can prove
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mathematically that an instability occurs
in this case. The reason is that we have
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an feedback between the grounding line
retreat and the ice locks across the
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grounding line. If the grounding line
retreats in a case where we have a
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retrograde sloping bed and the ice is
ground below sea level, that means that
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the ice thickness towards the interior is
larger. And this generally also means that
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the ice flux across the grounding line is
larger, leading to further retreat off the
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grounding line and so on and so on. So
again, we have a positive feedback
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mechanism that could drive self-sustained
ice loss from parts of the West and East
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Antarctic ice sheet. And the concern is
now that this marine ice sheet instability
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is potentially underway in the Amundson
basin here in West Antarctica. Now, what's
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unclear is, how fast this change would
actually occur. So if we have actually
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triggered the marine ice sheet instability
in this region, and that means we have a
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committed ice loss of roughly one meter
sea level equivalent, then the question is
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still, how fast does this occur? And for
this, it really matters how much further
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global warming continues. So and at which
rate the temperature will change in the
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future. So this is what's happening in
part of the West Antarctic ice sheet. We
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were also asking ourselves, weather could
something like this also happen for East
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Antarctica and how stable are each of the
different ice basins in Antarctica? So we
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did something of a stability check on the
Antarctic ice sheet to assess the risk of
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long term sea level rise from these
different regions. What you will see next
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is an animation where we're increasing the
global mean temperature, but we're
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increasing it very, very slowly, at a much
slower rate than the typical rate of
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change in the ice sheet to test for the
stability of these different parts. And
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what we see is that at roughly 2°C, we are
losing a large part of the West Antarctic
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ice sheet. So there's a first tipping
point around 2°C. And then as the
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temperature increases, also the surface
elevation is lowered. And that leads to,
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potentially then also triggering these
surface elevation and melt elevation
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feedbacks in East Antarctica. So around
6°C to 9°C, there's another major
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threshold. And after this, large parts of
the East Antarctic ice sheet could also be
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committed to long term sea level rise. At
about 10°C, the Antarctic ice sheet could
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potentially become ice free on the long
term. And, this is really important. What
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we're seeing here are not projections, but
what we're seeing here is a stability
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check. So we're not looking at something
that's happening within the next century
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or so, but rather we're interested in
understanding, at which temperatures the
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Antarctic ice sheet could still survive on
the long term. We also wanted to see if
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some of these changes are reversible. And
what we find is a so-called hysteresis
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behavior of the Antarctic ice sheet. That
means, as we're losing the ice and we'll
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then cool the temperatures back down, the
ice sheet does not regrow back to its
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initial state, but it takes much, much
colder temperatures to regrow the same ice
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sheet volume that we are currently having
at present day temperature levels. So
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there's a significant difference between
this retreat and the regrowth path. And
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this can be up to 20 meters of sea level
equivalent in the difference between these
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two paths. What this looks like
regionally, you can see here. So again, we
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have the retreat and the regrowth path at
2°C of global warming, and 4°C of global
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warming. So these are the long term
effects at these temperature levels. And
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you can see that, for instance, for 4°C
large parts of East Antarctic and also of
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the West Antarctic ice sheet do not regrow
at the same temperature level. So we
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clearly observe this hysteresis behavior.
That's another sign that the Antarctic ice
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sheet is the tipping element in the
climate system. So both Greenland and
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Antarctica are tipping elements in the
climate system. There are a number more
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candidates for tipping elements, including
some of the larger biosphere components,
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for instance, the Amazon rainforest, the
tropical coral reefs, and also the boreal
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forests, as well as some of the large
scale circulations. So, for instance, the
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Atlantic thermohaline circulation, what we
often term the Gulf Stream, and the Indian
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summer monsoon are tipping candidates in
the climate system. Now, if we go back to
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our temperature evolution since last
glacial maximum, and we now insert what we
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know about the tipping thresholds of these
different components in the Earth system,
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then this is what we get. And we see, that
there are basically three clusters of
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tipping elements in comparison to the
global mean temperature here. And you see
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in these burning ember diagrams that some
of these tipping elements are at risk of
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switching into a different state, even
within the Paris range of 1.5 - 2°C of
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warming. And among these most vulnerable
tipping elements are the West Antarctic
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ice sheet and the Greenland ice sheet and
in general, the cryosphere elements which
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seem to react to global warming and
climate change much faster and therefore
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belong to the most vulnerable parts of the
Earth system. So, if there's one thing
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that I would like you to take away from
this talk, it is that ice matters. I've
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presented you with three reasons why.
First of all, polar ice acts as a climate
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archive. It also acts as an early warning
system. Secondly, glaciers and ice sheets
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are important contributors already to
current sea level rise, but they will
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become even more important in the future
as the global mean temperature keeps
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rising. And thirdly, both Greenland and
Antarctica are tipping elements in the
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Earth system. And one of the next things
we need to understand is how these tipping
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elements interact with one another.
Because we have a very good understanding
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by now of the different mechanisms behind
these tipping elements and of the
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individual temperature thresholds. But one
of the, I think, most important questions
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we need to ask ourselves, is how the
interaction of the tipping elements
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changes the stability of the Earth system
as a whole and if there could be something
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like domino effects in the Earth system.
And with this, thank you so much for your
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attention. And I'm very much looking
forward to questions.
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Herald: Yeah, OK, fine, good, läuft, könnt
ihr mich also hör'n, und ihr müsst mir
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also sagen, wann ich wieder drauf bin.
Off: Du bist live.
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H: Hallo, wilkommen zurück! Thanks for
this awesome talk, Ricarda, and we are now
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going to have a Q&A. And if you have any
questions regarding this awesome talk,
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then please post them to the signal
angels. They are following on Twitter and
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the Fediverse here, using the hashtag
#rc3one, because this is rc1. And you can
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also post your questions to the IRC. You
know, I already have a first question. I
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don't know, Ricarda, if you can hear me,
but is there anything that this specific the CCC
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community of nerds and hackers can do more
than anyone else to help with this issue?
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What do you think that
we can do to help this?
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R: Yeah, thank you so much. Great
question. Let me start by saying I'm a
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nerd and hacker myself. I'm a developer,
or code developer, of the parallel ice
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sheet model. That's one of the ice sheet
models for Greenland and Antarctica that's
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being used around the globe with many
different applications. So, yeah, as a
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fellow nerd and hacker, I can say there's
lots we can do, in particular towards
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understanding even better the different
dynamics of the Greenland and the
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Antarctic ice sheet, but also beyond that,
for the Earth system as a whole. I think
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we're now at a point where we understand
the individual components of the Earth
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system better and better. We also have
better and better observations, satellite
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observations, but also observations at the
ground to further understand the different
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processes. But what we need now is to
combine this with our knowledge in the
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modeling community and also with some of
the approaches from big data, machine
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learning and so on, to really put this
together, all the different puzzle pieces
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to understand what this means for the
Earth system as a whole. And what I mean
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by that is, we now understand that there
are several individual tipping points in
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the Earth system. And we also know that as
global warming continues, we're at higher
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risks of transgressing individual tipping
points. But what we still need to
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understand is what does this mean for the
overall stability of our planet Earth?
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H: Thank you for this extended answer to
this question. I have another one. I would
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like to know, I mean, you showed a slide
where you showed the browning of the ice
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surface and then explained that this
speeds up the process of melting as well.
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But, can we just paint it white or with a
reflective paint on it? Has this been
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simulated? Is this of interest to you
scientists?
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R: Yeah, very good question. So basically
what you're addressing here is the
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question of the so-called ice albedo
feedback. We all know this. As we're
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wearing black clothes in summer, it's
warmer than when we're wearing white
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clothes. And the same is basically true
for our planet as well. So the ice sheets
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and also the sea ice in the Arctic and
Antarctica, they contribute considerably
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to a net cooling still of the planet. So
if we didn't have these ice landscapes,
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that would mean that the planet would warm
even faster and even further than it
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already is today. So currently, the ice
albedo feedback is still helping us with
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keeping the temperatures at lower levels
than they would be without the ice
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landscapes. And, yeah, therefore, it is
definitely of interest to further
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understand what would this mean for, for
instance, the global mean temperature, but
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also regional changes, if we were to lose
our ice cover completely? And also the
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reverse question, of course, if we were to
whiten parts of the planet, then how would
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this affect temperature? One thing that we
found out is that if we were to lose the
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ice sheets and the sea ice in terms of the
ice albedo feedback alone entirely, then
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this could already lead to an additional
global warming of roughly 0.2°C. Now, that
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may not seem very much, but it certainly
is important in the grand scheme of
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things. As we're thinking of, for
instance, the Paris range of 1.5°C to 2°C
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of warming, every tenth of a degree
matters. So, yeah, very interesting
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question. And this is something that has
been done with numerical models, just to
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understand what kind of an effect these
kind of what-if-scenarios would have also
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in terms of the albedo.
H: Very interesting. So should we now
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start to develop drones
who can spray paint?
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R: laughs That's a good question. I
don't think that's the solution. I think
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we have a much better solution. And that
is we know that we need to to mitigate
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climate change and reduce greenhouse gas
emissions. And that is one that would work
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for sure. Whereas these questions of,
well, should we spray paint all of our
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buildings at the at the top white? That is
something that cannot be done at such a
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large scale as we would need it in order
to reverse global warming. And another
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thing to keep in mind is that even if we
were able to reduce the global signal,
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this still doesn't mean that we could also
reverse the regional scale changes. We're
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already experiencing a large increase in
extreme weather and climate events. And
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that is certainly something that I haven't
seen so far, that this could also be
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reversed just by reversing the global mean
temperature change as a whole.
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H: I have another question. I think that's
quite interesting. How old is the oldest
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ice in Antarctica? Are you aware of that?
And how long would it take a minimum to
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lose that entirely?
R: Yeah, very good question. So the oldest
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ice, there's actually an ongoing search
for the oldest ice in Antarctica. So to
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say, we know that Antarctica was ice free
for the last time, roughly 34 million
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years ago. So when we're talking about
these scenarios that eventually Antarctica
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could become ice free with, of course,
very strong global warming scenarios of
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about 10°C of global warming, then we need
to keep in mind that this was the case for
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the last time, about 34 million
years ago. Now, as we're speaking, there
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is an ongoing project, an international
collaboration to find and and also drill
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for the oldest ice so that we can really
understand our Earth's history better and
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better. And so this is a very exciting
project because, as I said, the ice cores
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are kind of like tree rings and we can
count back in time and really understand
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what our global climate was like several,
hundreds of thousands of years ago. So,
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yeah, with that being said, I think it's
important to keep in mind that this is
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something that humans certainly have never
experienced and that's therefore
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unprecedented in our world.
H: ...for this very elaborate answer to
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this question, I know it is not the core
of your research, but someone from the
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internet asked, if it's possible for old
viruses and all the bacteria from back
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when Antarctica was like beginning to
freeze over or from like
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millions of years ago, is it possible for
them to thaw out again? Is that a danger
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for us?
R: Oh, that's also a very interesting
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question. So I'm no expert on this, but I
could imagine that at the temperatures
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that we have, Antarctica, especially the
core ice body, there we have temperatures
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that go down to, well, I think the coldest
temperature was something like -90°C that
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was recorded there. But in any case, it's
very cold there. So there might be some
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bacteria that can survive these
conditions. And I've read about bacteria
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like that, but I wouldn't know that there
are many bacterial species or specimen
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that could survive these kinds of
conditions. So to be honest, I would have
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to read up on that. That's a very
interesting question.
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H: Yeah. Thank you for this answer. I
remember that you watched, that you showed
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an animation and a graph for a simulated
ice decline to find the tipping points in
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Antarctica. And on the x axis of that, I
couldn't see a time scale. And now someone
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asked on the internet, what are the
timescales between reaching a tipping
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point? And most of the ice being melted?
Is that years, decades, centuries,
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millennia? What's kind of the scale there?
R: Yes, very important point. So it's
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important to note that we're here showing
this over the global mean temperature
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change. And the reason for this is that
the way these kind of hysteresis
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experiments are run is that you have a
very slow temperature increase. So slow,
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in fact, that it's much slower than the
sort of internal time scales of the ice
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itself. And in this case, for instance, we
had a temperature increase of
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10^-4°C/year. And the reason for this is
because this is the way you're approaching
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the actual hysteresis curve that we were
interested in. So this should not be
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mistaken for sea level projections of any
sort. So what we find here are the actual,
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so to say, tipping points, the actual
critical thresholds, that parts of the
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Antarctic ice sheet cannot survive.
Nonetheless, of course, we're also working
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towards sea level projections and trying
to understand what kind of sea level
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change we can expect from the ice sheets
over the next decades to centuries to
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millennia. And one important thing there
is that most of the ice loss that could be
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triggered now, would actually happen after
the end of this century. So very often,
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when we see these sea level curves, we're
looking until the year 2100. So for the
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next decades, how does the sea level
respond to changes in temperature? But
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because we have so much inertia in the
system, that means that even if the global
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00:39:18,450 --> 00:39:24,140
warming signal was stopped right now, we
would still see continued sea level rise
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for several decades to centuries. And that
is something important to keep in mind. So
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I think we really need to start thinking
of sea level rise in terms of commitment
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rather than these short term predictions.
That being said, another important
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question and factor is the rate of sea
level change, because this is actually
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what we need to adapt to as civilizations.
When we think of building dams, there are
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two questions we need to answer. One is
the magnitude of sea level rise and and
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also in its upper scale and upper limit to
that. And the other question is the rate
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at which this changes. And what we find is
that on the long term, there is something
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like 2.3m/°C of sea level change. So this
is sort of a number to keep in mind when
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we think of sea level projections. And
yeah, I think it's really important to
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consider longer timescales than the one to
the year 2100 when we talk about sea level
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rise.
H: Thank you for this answer, very
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interesting and we are out of time now, so
thanks for all the questions and thank
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you, Ricarda, for this amazing talk. The
next talk on this stage will be about a
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related topic, measuring CO2 indoors, but
also in the atmosphere in general. But
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before that, we have a Herald News Show
for your prepared. So enjoy!
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Outro music
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